1. Field of the Invention
The invention relates to a method and device for imaging diffusion parameters of a body by means of magnetic resonance (MR).
2. Description of Related Art
In the context of the present application an MG (Meibohm, Gill) component is to be understood to mean a component of a transverse magnetization in the direction of a first axis of a rotating reference system, the magnetization being rotated about said first axis by the refocusing RF pulses. A method of the described kind is known form the article "Phase Insensitive Preparation of Single-Shot RARE: Application to diffusion Imaging in Humans", by D. C. Alsop, published in Magnetic Resonance in Medicine No. 38, pp. 527-533, 1997.
The known method is used for the in vivo imaging of diffusion phenomena in tissue of a human or animal body to be examined, for example the brain. The magnetization preparation pulse sequence of the known method includes, for example a gradient pair and a refocusing RF pulse for applying amplitude modulation which is dependent on diffusion of material in a part to be selected of the tissue of the body to be examined. An imaging pulse sequence which succeeds the magnetization preparation pulse sequence images the selected part of the tissue. The magnetic field gradients provide slice selection, phase encoding and frequency encoding of the MR signals, respectively. In order to reduce phase sensitivity in the successive MR signals, which sensitivity may be due to, for example motion of the body or motion of the tissue in the body during the magnetization preparation pulse sequence, a first crusher gradient is applied and the additional RF pulse is generated, respectively. The crusher gradient is a magnetic field gradient which causes a rotation of spins in such a manner that the magnetization due to the spins within a small area is distributed across the transverse plane relative to the steady magnetic field. The further first and second crusher gradients refocus and defocus the MG component. Subsequently, position-dependent MR signals are measured. A diffusion image of the selected part of the brain of the body to be examined is reconstructed from the measured position-dependent MR signals by means of two-dimensional transformation.
It is a drawback of the known method that artefacts occur in the image; for example, ghost images occur in the actual image of the part of the tissue. A ghost image is a second or subsequent image of the part of the tissue which has been shifted relative to the first image and has a reduced intensity.
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant's invention of the invention subsequently claimed.